This invention relates to electronic imaging systems, and, in particular, to an apparatus and method for quality assurance of images produced by such systems.
Electronic imaging systems are particularly versatile for producing special effect images. One such system, the Image Magic (TM) system of Eastman Kodak Company, enables a user to superimpose one image taken by a camera over another, stored, electronic video image. For example, such systems are particularly useful at public attractions where a person can have his own image superimposed on a background image identified with the attraction. An individual then stands in a studio in front of a solid color background and an electronic image of the individual is taken. A control unit for the system merges the image of the individual onto the stored, background image. The result is a composite image in which the individual appears to be standing in front of the background.
A particular problem encountered with such merged electronic images is shadows, particularly shadows cast by a person's face and other body parts. Such shadows can materially effect the quality of an image. The video characteristic associated with accurate shadow reproduction is known as pedestal. Pedestal is a video variable that controls the image quality of shadows. In particular, it controls the relationship of white, black and shadow to see that each one is distinguishable from the others. The pedestal is normally adjusted by the Operator of a video camera.
The quality of a shadow cast by a chin onto a person's neck is difficult to objectively evaluate. In one case, the chin shadow may be too dark and look like a beard. In another case, the chin shadow may be too light and so the jaw of the person's face lacks depth. Present systems rely on the operator's subjective judgment of what is an acceptable pedestal.
In addition to the problem of pedestal adjustment, electronic imaging systems also require quality standards for exposure, focus, color, gamma, and linear matrix. Pedestal, gamma, and linear matrix are parameters that are characteristic of video systems. While pedestal refers to shadows or black images, gamma refers to the darkness of the overall target. Thus, with too much gamma, the image appears very saturated and the colors and blacks are too deep. An incorrect linear matrix results in an image where the colors appear slightly washed out. As such, the image has too light an appearance.
Until now there has been no quality standard for assuring the pedestal, gamma, and linear matrix characteristics of images, in particular, composite electronic images.